This type of but it takes a lot of time and different steps but you can do it.
let
C be the number of children
A be the number of adults
S be the number of seniors
Write down everything you were given in the problem
C ($7) + A ( $11) + S ($9) = $2116 You know how much was paid given the price per ticket.
C + A + S = 224 You know the total number of people who attended the show
A+S =176 You know the number of Adults and Seniors
So, know you need to solve for C,A,S.
If A+S =176, then you can substitute that in the second equation above and rewrite it as:
C + (176)= 224
So, C = 48
then substitute 48 for C in the first equation
48 ($7) + A ( $11) + S ($9) = $2116
$336 + A ($11) + S ( $9) = $2116
now subtract $336 from both sides
A ($11) + S($9) = $1780
remember that you know that A + S = 176 ( see above)
So you know have two equations with two unknowns.
A ($11) + S($9) = $1780
A + S =176
now you use substitution
subtract S from both sides and you get
A= 176-S
You that to solve
A ($11) + S($9) = $1780
( 176-S) ($11) + S($9) =$1780
use the distributive property to multiply
$1936-S($11) +S($9) =$1780
1936-S(11) +S(9)=1780 ( I dropped the dollar signs for now)
you know want to solve for S
combine the Ss and move them to one side of the equation
1936-2S=1780
1936-1780= 2S
156 =2S
78 =S
and since you know that S + A = 176
then A = 98
So, there you have it.
C=48
A=98
S=78